An electrophotographic image forming apparatus which uses a two-component developer composed of toner and a carrier exercises control to keep a constant toner density at all times by detecting the two-component developer in a developing portion with a permeability sensor and, when the density thereof becomes low, resupplying toner to the developer from a toner cartridge having a housing in which the toner is stored. In this control, in the case where a condition that the toner density is lower than a predetermined reference density continues for a specified time or more, the apparatus determines that there is no toner in the housing, gives a warning that there is no toner in the housing to the operator, and urges the operator to replenish the image forming apparatus with toner.
In this control, however, since notification representing that toner is exhausted is suddenly performed, the operator takes time to prepare for replenishment with toner and replacement of the toner cartridge, which results in that the image forming apparatus cannot be used for a long period during this replenishing operation. Accordingly, a technique for making it possible to securely detect the remaining amount of toner in the housing of the toner cartridge is required.
A first related art of such a technique is a copying machine equipped with a permeability sensor which detects the permeability of a developer supplied from the developing portion to a photoreceptor drum and an optical density sensor which detects the surface density of the photoreceptor drum subjected to development by the developing portion {refer to Japanese Unexamined Patent Publication JP-A 2-280176 (1990), for example}. In this copying machine, by the use of both the two sensors of different kinds, that is, the permeability sensor and the optical density sensor, the remaining amount of toner in the toner cartridge storing the toner is detected based on the toner density of the developer supplied from the developing portion to the photoreceptor drum and the surface density of the photoreceptor drum.
Further, such a method can be considered as to determine that the reference amount of toner remaining in the toner cartridge is small or the toner is exhausted in the case where toner supplying means which supplies toner to the developing portion operates for a specified time or more. However, a wide variation exists in the supply reference amount per unit time of the toner supplying means among the individual image forming apparatuses, and there is a possibility that the variation results in errors in determination that the reference amount of toner remaining in the toner cartridge is small or the toner is exhausted. As a result, there is a possibility of incorrect determination that the remaining amount of toner is small or the toner is exhausted though a sufficient reference amount of toner remains in the toner cartridge, and contrarily, incorrect determination that toner remains sufficiently though toner in the toner cartridge is exhausted and an image formed on a recording sheet becomes lighter.
A second related art to avoid incorrect determination resulting from a variation in the toner supply reference amount per unit time of the toner supplying means among the individual image forming apparatuses as described above as far as possible is an image forming apparatus which detects the density of a developed image on the photoreceptor drum and, in the case where the detected image density is lower than a specified reference value, operates the toner supplying means {refer to Japanese Unexamined Patent Publication JP-A 9-197797 (1997), for example}. Consequently, based on the ratio between an operation time of the toner supplying means when the density of an image developed on the photoreceptor drum becomes the reference value or more and an operation time of the toner supplying means when the toner supply reference amount is the maximum, that is, based on the maximum resupply rate, the toner supply reference amount by the toner supplying means is regulated. Accordingly, it becomes possible to detect the reference amount of toner remaining in the toner cartridge.
FIG. 18 is a cross section view showing a toner cartridge 100 of a third related art. In the toner cartridge 100, a rotation axis 102 is provided in a storing space 101 that stores toner 200, so as to be capable of rotating around an axial line thereof L102. To the rotation axis 102, one end of a rotating portion 103 is connected. The rotating portion 103 is flexible and, to the other end, a permanent magnet piece 104 is disposed. When the rotation axis 102 rotates, the permanent magnet piece 104 of the rotating portion 103 also rotates around an axial line L101. To the external wall portion of a housing 105 of the toner cartridge 100, a magnetism detecting switch 106 is disposed.
Since the rotating portion 103 is flexible, the rotating portion bends meeting with resistance from the toner 200 while rotating around the axial line L102. A resistance force with which the rotating portion 103 meets from the toner 200 while rotating changes in response to the amount of the toner 200 stored in the storing space 101. Therefore, a movement path of the permanent magnetic piece 104 changes in response to the amount of the toner 200. For example, when the amount of the toner 200 in the toner cartridge 100 is large, the movement path becomes like a curved line C1 shown by a broken line in FIG. 18. When the amount of the toner 200 in the toner cartridge 100 becomes small, a resistance force with which the rotating portion 103 meets from the toner 200 becomes small, so that the bent rotating portion 103 is straightened linearly. Consequently, the movement path of the permanent magnetic piece 104 changes to become close to the housing 105 as becoming away from the axial line L102, and becomes a movement path like a curved line C2 shown by a chain double-dashed line in FIG. 18. At this moment, the permanent magnetic piece 104 of the rotating portion 103 passes through the vicinity of the magnetism detecting switch 106, so that the magnetism detecting switch 106 is turned on by magnetism formed by the permanent magnetic piece 104 of the rotating portion 103. Accordingly, it is detected that the toner 200 in the toner cartridge 100 is exhausted {refer to Japanese Unexamined Utility Model Publication JP-U 1-32049 (1989), for example}.
FIG. 19 is a cross section view showing a toner cartridge 100A of a fourth related art. Since the toner cartridge 100A has roughly the same configuration as the toner cartridge 100 of the third related art shown in FIG. 18 mentioned before except a rotating portion 103A connected to the rotation axis 102, the same components will be denoted by the same reference numerals, and a detailed description will be omitted. The rotating portion 103A connected to the rotation axis 102 of the toner cartridge 100A includes a supporting member 107 and a rotating member 108. One end of the supporting member 107 is connected to the rotation axis 102. One end of the rotating member 108 is connected to the other end of the supporting member 107 so as to be capable of making an angular displacement around an axial line L107 that passes through the other end and extends in parallel to the axial line L102 of the rotation axis 102. To the other end of the rotating member 108, the permanent magnet piece 104 is disposed. The supporting member 107 and the rotating member 108 is not flexible.
When the rotation axis 102 rotates around the axial line L102, the supporting member 107 and the rotating member 108 of the rotating portion 103A rotate, and the permanent magnet piece 104 of the rotating member 108 rotates. In the rotating portion 103A, the rotating member 108 is connected to the supporting member 107 so as to be capable of making an angular displacement, so that the movement path of the permanent magnet piece 104 disposed to the rotating member 108 becomes like a curved line C3 shown by a chain double-dashed line in FIG. 19 for the same reason as in the third related art mentioned before (refer to JP-U 1-32049, for example).
The copying machine of the first related art mentioned before detects the remaining amount of toner in the toner cartridge based on the permeability of the developer supplied from the developing portion to the photoreceptor drum and the surface density of the photoreceptor drum subjected to development by the developing portion, so that the copying machine detects that the remaining amount of toner in the toner cartridge is small, after at least the surface density of the photoreceptor drum decreases. Therefore, it is considerably difficult to prevent deterioration of an image formed on a recording sheet, in specific, decrease of the density of a formed image due to decrease of toner. Moreover, since the sensors of two kinds different from each other are used for detection of the remaining amount of toner, not only the manufacturing cost of the copying machine increases, but also the configuration and the control method of the copying machine become complicated.
Further, the rotating portion 103 of the toner cartridge 100 in the image forming apparatus of the second related art shown in FIG. 18 bends meeting with resistance from the toner 200 while rotating around the axial line L102 because the rotating portion 103 is flexible, but even if the amount of the toner is the same, depending on the condition of the toner, for example, in the case where the toner coheres partially, a resistance force with which the rotating portion 103 meets from the toner 200 changes, the bending state of the rotating portion 103 changes, and the movement path of the permanent magnet piece 104 changes. Therefore, the movement path of the permanent magnetic piece 104 in the toner 200 does not become fixed at all times, and there is a risk that although a sufficient amount of the toner 200 remains, the permanent magnet piece 104 is placed in the vicinity of the magnetism detecting switch 106 due to some factor and it is mistakenly detected that the toner is exhausted.
Further, although the rotating portion 103A of the toner cartridge 100A in the image forming apparatus of the third related art shown in FIG. 19 does not have flexibility, the rotating member 108 of the rotating portion 103A is capable of making an angular displacement around the axial line L107 parallel to the axial line L102 of the rotation axis 102, so that there is the same problem as in the aforementioned second related art.
FIG. 20 is a cross section view showing a state where the remaining amount of the toner 200 in the toner cartridge 100A of the third related art mentioned before is small. In the case where there is toner more outward in the radius direction than a movement path C4 of the other end of the supporting member 107 of the rotating member 103A shown by a chain two-dashed line when the rotating member 103A is rotating, when the rotation axis 102 rotates in a rotation direction C (clockwise in FIG. 20) around the axial line L102, the permanent magnet piece 104 moves sliding on an upper surface 200a of a toner layer. The radius of the movement path C3 of the permanent magnet piece 104 shown in FIG. 20 is shown in FIG. 19. The radius is smaller than the radius of the movement path C3 of the permanent magnet piece 104 in the case where the remaining amount of the toner 200 is larger than in the state shown in FIG. 20. Therefore, the distance from the permanent magnet piece 104 to the magnetism detecting switch 106 does not change in a manner that the distance becomes small as the remaining amount of the toner decreases, so that there is a possibility that the magnetism detecting switch 106 mistakenly detects the remaining amount of the toner 200.
Further, although such a method can be considered as to detect the dot number of an image to be formed on a recording sheet and detect the remaining amount of toner in the toner cartridge based on the detected dot number, the relation between the dot number and the consumption amount of the toner is easily affected by the surrounding environment, so that it is difficult to accurately detect the remaining amount of the toner.
Further, such a method can be considered as to dispose a light-transmitting transmission window, use an optical detecting sensor and detect the remaining amount of toner. However, in this toner cartridge, it is necessary to keep the transmission window in the state where the transmission window can transmit light at all times, with the result that means for cleaning the transmission window is necessary, and the structure of the toner cartridge becomes complicated. Moreover, the optical detecting sensor is easily affected by the light-transmitting state of the transmission window, and the detection accuracy is low.
Further, such a method can also be considered as to dispose a vibration detecting sensor to the toner cartridge, vibrate the housing and detect the remaining amount of toner based on the vibration state of the housing. However, in this toner cartridge, it is necessary to replace the vibration detecting sensor together with the toner cartridge, so that the manufacturing cost of the toner cartridge becomes extremely high.